The invention relates generally to x-ray tubes and, more particularly, to an apparatus for x-ray generation and a method of fabrication.
X-ray systems typically include an x-ray tube, a detector, and a bearing assembly to support the x-ray tube and the detector. In operation, an imaging table, on which an object is positioned, is located between the x-ray tube and the detector. The x-ray tube typically emits radiation, such as x-rays, toward the object. The radiation typically passes through the object on the imaging table and impinges on the detector. As radiation passes through the object, internal structures of the object cause spatial variances in the radiation received at the detector. The detector then emits data received, and the system translates the radiation variances into an image, which may be used to evaluate the internal structure of the object. One skilled in the art will recognize that the object may include, but is not limited to, a patient in a medical imaging procedure and an inanimate object as in, for instance, a package in an x-ray scanner or computed tomography (CT) package scanner.
X-ray tubes include a rotating anode structure for the purpose of distributing the heat generated at a focal spot. The anode is typically rotated by an induction motor having a cylindrical rotor built into a cantilevered axle that supports a disc-shaped anode target and an iron stator structure with copper windings that surrounds an elongated neck of the x-ray tube. The rotor of the rotating anode assembly is driven by the stator. An x-ray tube cathode provides a focused electron beam that is accelerated across a cathode-to-anode vacuum gap and produces x-rays upon impact with the anode. Because of the high temperatures generated when the electron beam strikes the target, the anode assembly may be rotated at a high rotational speed.
Between periods of x-ray production and periods of idle, the target material may experience a wide range of temperatures as it cools from operating temperature to room temperature. Within this wide range of temperatures, the target material may reach a temperature that represents the transition between a hot ductile state and a relatively cool brittle state, which may be referred to as a ductile-brittle transition temperature (DBTT). After a period of non-use, a warm-up scan may be used to preheat the target. A preheating scan allows the target to transition from the cooler brittle state to the warmer ductile state prior to high-power imaging protocols, thus reducing stress on the target material. However, due to operator error or scheduling requirements of the system, the preheating scan may be skipped, and the target material may drop below the DBTT, thus subjecting the target material to undesired stress and shortened target life.
Therefore, it would be desirable to have a method and apparatus to maintain an x-ray tube target within a desired temperature range and above the DBTT such that an imaging scanner may be used on demand without the need to perform a preheating scan.